Polygon mirror assembly, light scanning unit employing polygon mirror assembly, and image forming apparatus

ABSTRACT

A polygon mirror assembly, a light scanning unit employing the polygon mirror assembly, and an image forming apparatus. The polygon mirror assembly includes a polygon mirror formed of a plastic material and having a plurality of reflection surfaces; and a motor unit to support and rotate the polygon mirror, where the polygon mirror is coupled to the motor unit by using an adhesive material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No.10-2010-0117524, filed on Nov. 24, 2010, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

BACKGROUND

1. Field

The present disclosure relates to a polygon mirror assembly, a lightscanning unit employing the polygon mirror assembly, and an imageforming apparatus, and more particularly, to a polygon mirror assemblyincluding a plastic polygon mirror, a light scanning unit employing thepolygon mirror assembly, and an image forming apparatus.

2. Description of the Related Art

Light scanning units that are employed in electrophotographic imageforming apparatuses such as laser printers, digital photocopy machines,and facsimile machines deflect a light beam emitted from a light sourceto which an image signal is applied and scan the light beam in a mainscanning direction of an image carrier. Electrostatic images are formedon image carriers by using the light scanning units in a main scanningdirection and by movement of the image carriers in a sub scanningdirection.

A light scanning unit includes a polygon mirror assembly for deflectinga light beam emitted from a light source in a predetermined direction. Aconventional polygon mirror is generally produced through ultraprecisionmachining using high-purity aluminum having a purity of more than 99% inorder to obtain a reflectivity of more than 85%. The polygon mirrorassembly formed of the high-purity aluminum has problems such as a highmanufacturing cost and difficulty in adjusting production volume.

SUMMARY

The present disclosure provides a polygon mirror assembly that uses aplastic polygon mirror and may minimize performance degradationoccurring during assembling, a light scanning unit employing the polygonmirror assembly, and an image forming apparatus.

According to an aspect of the present disclosure, there is provided apolygon mirror assembly including: a polygon mirror formed of a plasticmaterial and having a plurality of reflection surfaces; and a motor unitto support and rotate the polygon mirror, wherein the polygon mirror iscoupled to the motor unit by using an adhesive material.

A holder frame may be coupled to a rotation axis of the motor unit, andthe polygon mirror may be coupled to the holder frame by using theadhesive material. The polygon mirror may include a hole, and a part ofthe holder frame is inserted into the hole of the polygon mirror, andthe adhesive material may be uniformly coated on at least one of aninner surface of the polygon mirror defining the hole and an outersurface of the holder frame contacting the inner surface.

A tilt preventing groove having a space for accommodating the adhesivematerial may be formed in the holder frame. The tilt preventing groovemay be a groove formed on a surface of the holder frame around the partof the holder frame inserted into the hole of the polygon mirror.

A tilt preventing step having a space for accommodating the adhesivematerial may be formed in the inner surface of the polygon mirror. Thetilt preventing step may be a groove formed on a lower circumferentialsurface of the inner surface of the polygon mirror.

The polygon mirror may include a hole, a rotation axis of the motor unitmay be inserted into the hole of the polygon mirror, and the adhesivematerial may be uniformly coated on at least one of an inner surface ofthe polygon mirror defining the hole and the rotation axis of the motorunit.

The adhesive material may be any one selected from the group consistingof an ultraviolet (UV)-curable adhesive material, a heat-curableadhesive material, and an instant adhesive material.

A reflection layer may be formed on each of the plurality of reflectionsurfaces.

According to another aspect of the present disclosure, there is provideda light scanning unit including: a light source to emit a light beam; apolygon mirror assembly to deflect the light beam emitted from the lightsource in a main scanning direction; an imaging optical unit to imagethe light beam deflected by the polygon mirror assembly onto a surfacethat is to be scanned, wherein the polygon mirror assembly is formed ofa plastic material and includes a polygon mirror having a plurality ofreflection surfaces and a motor unit to support and rotate the polygonmirror, and wherein the polygon mirror is coupled to the motor unit byusing an adhesive material.

According to another aspect of the present disclosure, there is providedan image forming apparatus including: a light scanning unit including: alight source to emit a light beam; a polygon mirror assembly to deflectthe light beam emitted from the light source in a main scanningdirection; an imaging optical unit to image the light beam deflected bythe polygon mirror assembly onto a surface that is to be scanned; adeveloping unit disposed on a focusing point of the light beam emittedfrom the light scanning unit, and including a plurality ofphotoreceptors on each of which an electrostatic latent image is formedand a developing roller to develop the electrostatic latent image formedon each of the photoreceptors; and a transfer unit to transfer an imagedeveloped by the developing unit, wherein the polygon mirror assembly isformed of a plastic material, includes a polygon mirror having aplurality of reflection surfaces and a motor unit to support and rotatethe polygon mirror, and wherein the polygon mirror is coupled to themotor unit by using an adhesive material.

The polygon mirror assembly, the light scanning unit employing thepolygon mirror assembly, and the image forming apparatus suppressoptical performance degradation by minimizing deformation that may occurwhen the polygon mirror formed of a plastic material is assembled.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present disclosurewill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIG. 1 is a schematic view of a light scanning unit according to anembodiment of the present disclosure;

FIG. 2 is a schematic cross-sectional view of a polygon mirror assemblyemployed in the light scanning unit of FIG. 1;

FIG. 3 is another example of the polygon mirror assembly of FIG. 2;

FIG. 4 is another example of the polygon mirror assembly of FIG. 2;

FIG. 5 is a view illustrating the polygon mirror assembly of FIG. 2, inwhich a polygon mirror tilts due to an adhesive material discharged fromthe polygon mirror assembly of FIG. 2; and

FIG. 6 is a schematic view of an electrophotographic image formingapparatus according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

Hereinafter, the present disclosure will now be described more fullywith reference to the accompanying drawings, in which exemplaryembodiments of the disclosure are shown. In the drawings, like referencenumerals denote like elements, and a size of each component isexaggerated for convenience and clarity.

FIG. 1 is a schematic view of a light scanning unit employing a polygonmirror assembly 10, according to an embodiment of the presentdisclosure. FIG. 2 is a schematic cross-sectional view of the polygonmirror assembly 10 of the current embodiment.

Referring to FIG. 1, the light scanning unit includes a light source 1;the polygon mirror assembly 10 including a rotational polygon mirror 11,and a scanning lens 7.

The light source 1 emits a light beam and may be a semiconductor laserdiode for emitting a laser beam. The light source 1 may emit a singlelight beam or a plurality of light beams. FIG. 1 illustrates the lightsource 1 emitting a single light beam. If the light source 1 emits aplurality of light beams, the light beams may be incident on one of aplurality of reflection surfaces 11 a at different incident angles orincident on a plurality of the reflection surfaces 11 a.

A collimating lens 2 may be disposed on an optical path between thelight source 1 and the polygon mirror 11. The collimating lens 2collimates light emitted from the light source 1. A cylindrical lens 4may further be disposed on an optical path between the collimating lens2 and the polygon mirror 11. The cylindrical lens 4, that is, an opticalunit having a predetermined power in only a sub scanning direction,focuses a light beam from the collimating lens 2 onto a reflectionsurface 11 a of the polygon mirror 11 in the sub scanning direction. Anaperture stopper 3 may further be disposed between the collimating lens2 and the cylindrical lens 4 to adjust a diameter of a light beam. Thecollimating lens 2, the aperture stopper 3, and the cylindrical lens 4constitute an incident optical unit of the light scanning unit.

The scanning lens 7, that is, an imaging optical unit having aconvergence function and fθ lens characteristics, images a light beamthat is deflected and scanned by the polygon mirror 11 onto an outercircumferential surface of a photoreceptor 9 at a constant speed. FIG. 1illustrates one scanning lens 7 as the imaging optical unit. However,the imaging optical unit may include 2 or more lenses. A mirror 8 is anexample of an optical path changing unit that changes an optical path ofa scanned light beam.

Referring to FIG. 2, the polygon mirror assembly 10 includes the polygonmirror 11, a holder frame 12, and a motor unit 14.

The polygon mirror 11 includes four reflection surfaces 11 a formed onan outer surface of the polygon mirror 11 and an inner surface 11 bdefining a hole formed in a center portion of the polygon mirror 11. Theinner surface 11 b of the polygon mirror 11 and an outer surface of theholder frame 12 contacting the inner surface 11 b are coupled to eachother through an adhesive material 13. The polygon mirror 11 may beformed of plastic, such as epoxy, by using an injection molding process.As the polygon mirror 11 is formed of a plastic material, a materialcost of the polygon mirror 11 may be decreased and mass production ofthe polygon mirror 11 may be easily performed. The adhesive material 13may be any of an ultraviolet (UV)-curable adhesive material, aheat-curable adhesive material, an instant adhesive material, and thelike. For example, when the adhesive material 13 is a UV-curableadhesive material, the adhesive material 13 is coated on the innersurface 11 b of the polygon mirror 11 and the outer surface of theholder frame 12 contacting the inner surface 11 b, the polygon mirror 11and the holder frame 12 are coupled to each other, and UV light is thenirradiated thereon by using a UV lamp to rapidly harden the adhesivematerial 13, thereby fixing the polygon mirror 11 and the holder frame12.

Meanwhile, a metal layer with a high reflectivity formed of, forexample, aluminum (Al) or silver (Ag) may be attached on each reflectionsurface 11 a. In order to protect the metal layer from externalenvironment and to prevent oxidization of the metal layer, a protectionlayer, for example, a SiO₂ layer, may further be prepared on the metallayer. The number of reflection surfaces 11 a shown is just an example,and the present disclosure is not limited to four reflection surfaces 11a. Also, the inner surface 11 b of the polygon mirror 11 and the outersurface of the holder frame 12 contacting the inner surface 11 b mayhave a cylindrical shape for convenience of assembling, but the presentdisclosure is not limited thereto. For example, the inner surface 11 bof the polygon mirror 11 and the outer surface of the holder frame 12contacting the inner surface 11 b may have a polygonal shape, forexample, a quadrangle shape.

Meanwhile, the motor unit 14 includes a bearing holder 18 fixed to aprinted circuit board 21, an electromagnet 19 disposed on acircumferential surface of the bearing holder 18, a shaft 17 as arotation axis formed in the bearing holder 18 and able to revolve, abushing 20 disposed between the bearing holder 18 and the shaft 17, arotor housing 15 coupled to the shaft 17, and a permanent magnet 16disposed inside the rotor housing 15 and facing the electromagnet 19.

However, in a conventional polygon mirror assembly, a polygon mirror isfixed to a holder frame or a motor unit by using a flat spring. Eventhough an elastic force from the flat spring deforms the polygon mirror,the conventional polygon mirror is generally formed of a metal such asAl, and thus the deformation due to the flat spring may beinsignificant. However, the inventors have found that if the polygonmirror 11 is formed of plastic, using a flat spring to attach thepolygon mirror 11 considerably deforms the polygon mirror 11. In otherwords, even though a polygon mirror formed of a metal is attachedthrough spring insertion, since the Young's modulus thereof issufficiently great, a deformation amount is not significant. On theother hand, a polygon mirror formed of a plastic material has a smallYoung's modulus, and thus a deformation amount due to spring insertionis great.

Table 1 shows deformation amounts of reflection surfaces of a polygonmirror formed of a plastic material due to spring insertion.

TABLE 1 initial reflection reflection surface surface PV (μm)Deformation surface PV (μm) after assembling amount (μm) 1 0.392 1.2200.828 2 0.341 2.993 2.652 3 0.343 1.485 1.142 4 0.366 3.102 2.736average 0.361 2.200 1.840

Here, the reflection surface process variables (PV) each denote adeviation between a maximum value and a minimum value with respect to anentire area of a reflection surface, that is, flatness. Referring toTable 1, the average deformation amount of the reflection surfaces ofthe polygon mirror formed of a plastic material is about 1.840 μm.However, since a permissible deformation amount of the polygon mirror isto be within the range of about 0.2 μm to about 0.3 μm, the deformationamount due to the spring insertion greatly exceeds the permissibleamount, and thus it is difficult to apply a method of attaching theconventional polygon mirror formed of a metal to the polygon mirrorformed of plastic.

Thus, as described in the current embodiment, stress applied to thepolygon mirror 11 during assembling may be minimized by coupling thepolygon mirror 11 and the holder frame 12 to each other by using theadhesive material 13. As such, deformation of the reflection surfaces 11a of the polygon mirror 11 during assembling may be minimized byminimizing stress applied to the polygon mirror 11 during assembling,thereby preventing performance degradation of the light scanning unit.

Table 2 shows deformation amounts of the reflection surfaces 11 a of thepolygon mirror 11 formed of a plastic material during assembling usingthe adhesive material 13.

TABLE 2 reflection initial surface reflection PV (μm) deformationsurface after amount sample no. surface PV (μm) assembling (μm) 1 10.480 0.581 0.101 2 0.386 0.321 −0.065 3 0.466 0.460 −0.006 4 0.4260.478 0.052 2 1 0.477 0.733 0.256 2 0.399 0.405 0.006 3 0.443 0.7030.260 4 0.447 0.360 −0.087 3 1 0.422 0.740 0.318 2 0.347 0.386 0.039 30.421 0.837 0.416 4 0.398 0.505 0.107 4 1 0.482 0.431 −0.051 2 0.2930.452 0.159 3 0.647 0.412 −0.235 4 0.302 0.372 0.070 5 1 0.497 0.9370.440 2 0.323 0.319 −0.004 3 0.472 0.613 0.141 4 0.345 0.336 −0.009average 0.424 0.519 0.095

Here, the reflection surface process variables (PV) each denote adeviation between a maximum value and a minimum value of a deformationamount with respect to an entire area of a reflection surface. Referringto Table 2, when the polygon mirror 11 is coupled to the holder frame 12by using the adhesive material 13, the average deformation amountoccurring during assembling among the reflection surfaces 11 a of thepolygon mirror 11 formed of a plastic material is just about 0.095 μm,and thus a general permissible deformation amount of the polygon mirror11 is within the range of about 0.2 μm to about 0.3 μm.

Even though the deformation amount of each reflection surface 11 a isremarkably improved by using the adhesive material 13, deformationamounts of the reflection surface 11 a due to contraction of theadhesive material 13 may still exist. If the adhesive material 13 ispartially coated on an upper portion or a lower portion of the innersurface 11 b of the polygon mirror 11, the polygon mirror 11 may bepartially deformed. Accordingly, in order to make deformationdistribution of the polygon mirror 11 uniform, the adhesive material 13is uniformly coated on the inner surface 11 b of the polygon mirror 11or on the outer surface of the holder frame 12 contacting the innersurface 11 b.

Referring back to FIGS. 1 and 2, operations of the light scanning unitof the current embodiment will be described below.

Light emitted from the light source 1 passes through the collimatinglens 2, the aperture stopper 3, and the cylindrical lens 4 sequentiallyin the order stated, and is then irradiated onto the reflection surface11 a of the polygon mirror 11. The light reflected by the reflectionsurface 11 a of the polygon mirror 11 passes through the scanning lens7, is deflected by the mirror 8, and then is irradiated onto the surfaceof the photoreceptor 9. If power is supplied to the electromagnet 19 ofthe motor unit 14, the rotor housing 15 rotates about the shaft 17 dueto an electromagnetic interaction between the electromagnet 19 and thepermanent magnet 16. The holder frame 12 is coupled to and rotatestogether with the rotor housing 15 and the shaft 17, and the polygonmirror 11 adhered to the holder frame 12 rotates together with theholder frame 12, the rotor housing 15, and the shaft 17. As such, whenthe polygon mirror 11 rotates due to driving of the motor unit 14, thelight reflected by the reflection surface 11 a of the polygon mirror 11is scanned in a direction perpendicular to a rotation axis of thepolygon mirror 11, that is, in a main scanning direction. Meanwhile, thephotoreceptor 9 moves its scanned surface in a direction perpendicularto the direction in which the photoreceptor 9 is scanned by the polygonmirror 11. Accordingly, an electrostatic latent image comprised ofexposed regions and unexposed regions is formed on the scanned surfaceof the photoreceptor 9 by turning on and off the light source 1.

Hereinafter, other examples of the polygon mirror assembly 10 of thecurrent embodiment will be described below.

FIG. 3 illustrates another example of the polygon mirror assembly 10 ofFIG. 2. Referring to FIG. 3, the polygon mirror assembly 10 of thecurrent embodiment includes a plurality of tilt preventing grooves 12 aformed in a holder frame 12′. The tilt preventing grooves 12 a may beformed to have a predetermined depth in at least a part of a surface ofthe holder frame 12′ around a projection portion inserted into the innersurface 11 b of the polygon mirror 11. The tilt preventing grooves 12 aof the holder frame 12′ may receive the adhesive material 13 dischargedfrom between surfaces of the polygon mirror 11 and the holder frame 12′that contact each other.

FIG. 4 illustrates another example of the polygon mirror assembly 10 ofFIG. 2. Referring to FIG. 4, the polygon mirror assembly 10 of thecurrent embodiment includes a plurality of tilt preventing steps 11 cformed in an inner surface 11 b of a polygon mirror 11′. The tiltpreventing steps 11 c may be formed to have a predetermined depth in atleast a part of a lower circumferential surface of the inner surface 11b of the polygon mirror 11′. The tilt preventing steps 11 c of thepolygon mirror 11′ may receive the adhesive material 13 discharged frombetween surfaces of the polygon mirror 11′ and the holder frame 12 thatcontact each other.

Referring to FIG. 5, when the polygon mirror 11 is coupled to the holderframe 12 by using the adhesive material 13, a part 13 a of the adhesivematerial 13 may harden after being discharged downward from between theinner surface 11 b of the polygon mirror 11 and the outer surface of theholder frame 12 contacting the inner surface 11 b. As such, thedischarged adhesive material 13 a may tilt the polygon mirror 11 to oneside. Due to the tilt of the polygon mirror 11, error amounts of a doton a sheet of paper on which an image is printed in a vertical directionare obtained as shown in Table 3.

TABLE 3 difference in vertical DPA (″) direction (μm) 600 15 300 7.1 1203 60 1.5 0 0

In Table 3, the dynamic pyramidal angles (DPA) each denote a slant of arotation axis of the motor unit 14, that is, a tilt amount of the shaft17 and the reflection surface 11 a, and the DPA is in units of seconds(″). As shown in Table 3, the tilt of the polygon mirror 11 due to thedischarged adhesive material 13 a causes blurring of dots printed on asheet of paper, thereby degrading a picture quality. Thus, as shown inthe examples illustrated in FIGS. 3 and 4, tilt due to the dischargedadhesive material 13 a may be prevented through the tilt preventinggrooves 12 a or the tilt preventing steps 11 c of the polygon mirror11′.

In the above-described embodiments and other examples, the polygonmirrors 11 and 11′ are coupled to the motor unit 14 through the holderframes 12 and 12′, but the present disclosure is not limited thereto.The holder frames 12 and 12′ may be omitted, and the shaft 17 of themotor unit 14 may be directly coupled to the polygon mirrors 11 and 11′by using the adhesive material 13.

FIG. 6 is an example of an image forming apparatus employing the lightscanning unit of the current embodiment.

The image forming apparatus illustrated in FIG. 6 is a dryelectrophotographic image forming apparatus for printing a color imageby using a dry developer (hereinafter, referred to as toner).

The image forming apparatus includes a light scanning unit 100, aplurality of developing units 200, a transfer unit 300, and a fixingunit 400.

The light scanning unit 100 may be the light scanning unit describedabove. In order to print a color image, the light scanning unit 100scans a plurality of light beams, and the plurality of developing units200, one for each of colors to be printed, may be formed to correspondto the plurality of light beams. In this regard, the light scanning unit100 may include a plurality of light scanning units or maysimultaneously scan a plurality of light beams using one polygon mirrorassembly, as described above with reference to FIG. 1. For example, thelight scanning unit 100 may scan four light beams corresponding to black(K), magenta (M), yellow (Y), and cyan (C), and four developing units200 for black (K), magenta (M), yellow (Y), and cyan (C) may be formed.

The developing units 200 each include a photosensitive drum 210, thatis, an image receptor, on which an electrostatic latent image is formedand a developing roller 220 for developing the electrostatic latentimage.

The photosensitive drum 210, that is, a photoreceptor, may be acylindrical metal pipe having a photosensitive layer that has apredetermined thickness and that is formed on an outer circumference ofthe cylindrical metal pipe. Although not shown herein, a photosensitivebelt may be employed as the photoreceptor. The outer circumference ofthe photosensitive drum 210 is a surface that is to be exposed. A chargeroller 230 is disposed on the outer circumference of the photosensitivedrum 210 on a portion of the outer circumference of the photosensitivedrum 210 upstream from a region of the outer circumference that is to beexposed to the light scanning unit 100. The charge roller 230 is acharging unit that contacts the photosensitive drum 210 and rotates toapply a uniform charge to the surface of the photosensitive drum 210. Acharge bias is applied to the charge roller 230. A corona charging unit(not shown) may be used instead of the charge roller 230.

The developing roller 220 supplies toner adhered to its outercircumference to the photosensitive drum 210. A development bias isapplied to the developing roller 220 to supply toner to thephotosensitive drum 210. Although it is not illustrated in the drawings,the developing units 200 may further include a supply roller forallowing toner contained in the developing units 200 to adhere to thedeveloping roller 220, a restriction unit for restricting an amount ofthe toner adhered to the developing roller 220, and an agitator fortransferring the toner contained in each of the developing units 200 tothe supply roller and/or the developing roller 220.

The transfer unit 300 may include a paper transfer belt 310 and fourtransfer rollers 320. The paper transfer belt 310 is arranged to face aregion of the outer circumference of the photosensitive drum 210 exposedout of each developing unit 200. The paper transfer belt 310 circulatesby being supported by a plurality of support rollers 330, 340, 350, and360. The four transfer rollers 320 are arranged to face thephotosensitive drum 210 of each developing unit 200 with the papertransfer belt 310 interposed therebetween. A transfer bias is applied toeach of the transfer rollers 320.

A color image forming process that may be performed theelectrophotographic image forming apparatus configured as detailed abovewill be described.

The photosensitive drum 210 of each developing unit 200 is charged tohave a uniform electric potential by a charge bias applied to the chargeroller 230. The light scanning unit 100 scans four light beamscorresponding to image information of cyan (C), magenta (M), yellow (Y),and black (K) colors to each photosensitive drum 210 of the developingunits 200 to form electrostatic latent image. A development bias isapplied to the developing roller 220. Then, toner adhered to the outercircumference of the developing roller 220 adheres to the electrostaticlatent image on the photosensitive drum 210 and thus toner images ofcyan, magenta, yellow, and black may be respectively formed on thephotosensitive drums 210 of the developing units 200.

A medium that finally receives toner, for example, a paper P, is ejectedfrom a cassette 500 by a pickup roller 510. The paper P is transferredto the paper transfer belt 510 by a transfer roller 520. The paper Padheres to a surface of the paper transfer belt 310 due to anelectrostatic force and is transferred at the same velocity as a runninglinear velocity of the paper transfer belt 310.

For example, a leading end of the paper P arrives at a transfer nip atthe same time as when a leading end of a toner image of cyan (C) formedon the outer circumferential surface of one photosensitive drum 210 ofone developing unit 200 arrives at the transfer nip facing one of thetransfer rollers 320. When a transfer bias is applied to the transferroller 320, the toner image formed on the photosensitive drum 210 istransferred to the paper P. As the paper P is transferred, toner imagesof magenta (M), yellow (Y), and black (K) formed on the photosensitivedrums 210 of the other developing units 200 are sequentially transferredto the paper P to overlap with one another. Accordingly, a color tonerimage is formed on the paper P.

The color toner image transferred to the paper P is maintained on asurface of the paper P due to an electrostatic force. The fixing device400 fixes the color toner image on the paper P using heat and pressure.The paper P after being subjected to the fixing process is ejected outof the image forming apparatus by an eject roller 530.

While the present disclosure has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

1. A polygon mirror assembly comprising: a polygon mirror formed of aplastic material and having a plurality of reflection surfaces; and amotor unit to support and rotate the polygon mirror, wherein the polygonmirror is coupled to the motor unit by using an adhesive material. 2.The polygon mirror assembly of claim 1, wherein a holder frame iscoupled to a rotation axis of the motor unit, and the polygon mirror iscoupled to the holder frame by using the adhesive material.
 3. Thepolygon mirror assembly of claim 2, wherein the polygon mirror comprisesa hole, and a part of the holder frame is inserted into the hole of thepolygon mirror, and the adhesive material is uniformly coated on atleast one of an inner surface of the polygon mirror defining the holeand an outer surface of the holder frame contacting the inner surface.4. The polygon mirror assembly of claim 3, wherein a tilt preventinggroove having a space to accommodate the adhesive material is formed inthe holder frame.
 5. The polygon mirror assembly of claim 4, wherein thetilt preventing groove is a groove formed on a surface of the holderframe around the part of the holder frame inserted into the hole of thepolygon mirror.
 6. The polygon mirror assembly of claim 3, wherein atilt preventing step having a space to accommodate the adhesive materialis formed in the inner surface of the polygon mirror.
 7. The polygonmirror assembly of claim 6, wherein the tilt preventing step is a grooveformed on a lower circumferential surface of the inner surface of thepolygon mirror.
 8. The polygon mirror assembly of claim 1, wherein thepolygon mirror comprises a hole, a rotation axis of the motor unit isinserted into the hole of the polygon mirror, and the adhesive materialis uniformly coated on at least one of an inner surface of the polygonmirror defining the hole and the rotation axis of the motor unit.
 9. Thepolygon mirror assembly of claim 1, wherein the adhesive material is anyone selected from the group consisting of an ultraviolet (UV)-curableadhesive material, a heat-curable adhesive material, and an instantadhesive material.
 10. The polygon mirror assembly of claim 1, wherein areflection layer is formed on each of the plurality of reflectionsurfaces.
 11. A light scanning unit comprising: a light source to emit alight beam; a polygon mirror assembly to deflect the light beam emittedfrom the light source in a main scanning direction; an imaging opticalunit to image the light beam deflected by the polygon mirror assemblyonto a surface that is to be scanned, wherein the polygon mirrorassembly is formed of a plastic material and comprises a polygon mirrorhaving a plurality of reflection surfaces and a motor unit to supportand rotate the polygon mirror, and wherein the polygon mirror is coupledto the motor unit by using an adhesive material.
 12. The light scanningunit of claim 11, wherein a holder frame is coupled to a rotation axisof the motor unit, and the polygon mirror is coupled to the holder frameby using the adhesive material.
 13. The light scanning unit of claim 12,wherein the polygon mirror comprises a hole, and a part of the holderframe is inserted into the hole of the polygon mirror, and the adhesivematerial is uniformly coated on at least one of an inner surface of thepolygon mirror to define the hole and an outer surface of the holderframe contacting the inner surface.
 14. The light scanning unit of claim13, wherein a tilt preventing groove having a space to accommodate theadhesive material is formed in the holder frame.
 15. The light scanningunit of claim 14, wherein the tilt preventing groove is a groove formedon a surface of the holder frame around the part of the holder frameinserted into the hole of the polygon mirror.
 16. The light scanningunit of claim 13, wherein a tilt preventing step having a space toaccommodate the adhesive material is formed in the inner surface of thepolygon mirror.
 17. The light scanning unit of claim 16, wherein thetilt preventing step is a groove formed on a lower circumferentialsurface of the inner surface of the polygon mirror.
 18. The lightscanning unit of claim 11, wherein the polygon mirror comprises a hole,a rotation axis of the motor unit is inserted into the hole of thepolygon mirror, and the adhesive material is uniformly coated on atleast one of an inner surface of the polygon mirror defining the holeand the rotation axis of the motor unit.
 19. The light scanning unit ofclaim 11, wherein the adhesive material is any one selected from thegroup consisting of an ultraviolet (UV)-curable adhesive material, aheat-curable adhesive material, and an instant adhesive material.
 20. Animage forming apparatus comprising: a light scanning unit comprising: alight source to emit a light beam; a polygon mirror assembly to deflectthe light beam emitted from the light source in a main scanningdirection; an imaging optical unit to image the light beam deflected bythe polygon mirror assembly onto a surface that is to be scanned; adeveloping unit disposed on a focusing point of the light beam emittedfrom the light scanning unit, and comprising a plurality ofphotoreceptors on each of which an electrostatic latent image is formedand a developing roller to develop the electrostatic latent image formedon each of the photoreceptors; and a transfer unit to transfer an imagedeveloped by the developing unit, wherein the polygon mirror assembly isformed of a plastic material, comprises a polygon mirror having aplurality of reflection surfaces and a motor unit to support and rotatethe polygon mirror, and wherein the polygon mirror is coupled to themotor unit by using an adhesive material.